An ice-free corridor sustained Arctic marine life during the last ice age, according to scientist from Norway and the UK

AN ICE FREE CORRIDOR SUSTAINED ARCTIC MARINE LIFE DURING THE LAST ICE AGE

Sea ice marginal zone in front of West Antarctic ice sheet. Polynias, ice free corridors between the sea ice and land based ice sheets, are common in Antarctica today. Photo: M. Forwick

During the last ice age, there was an ice free corridor wedged between two large ice masses in the Arctic. This corridor, which spanned several hundred kilometers, provided habitats for highly adaptable marine life-forms.

In a new study, scientists from Norway and the UK have shown that, 20,000 years ago, Arctic sea ice in the winter covered more than twice the area than it does today. Yet, there was a small ice-free oasis between ice covered continents and the frozen ocean. There, marine life prevailed.

“When we were looking for evidence of biological life in sediments at the bottom of the ocean, we found that between the sea ice covered oceans, and the ice sheets on land, there must have been a narrow ice-free corridor that extended over hundreds of kilometres into the Arctic. Such ice-free regions are often called “polynyas” – a Russian expression for an area of open water that is surrounded by sea ice and/or ice sheets,” says research scientist Jochen Knies from CAGE and the Geological Survey of Norway. 

The new findings, which were published recently in Nature Communications, also reveal that the polynya was sustained for at least 5,000 years, when the surroundings were largely covered by ice, and global ocean circulation was at a minimum.

Arctic oasis in front of the Eurasian ice sheet during the last Ice Age, 20.000 years ago (from Knies et al., 2018, Nature Communications).

Common today in Antarctica and Greenland

Today, polynyas are common around Antarctica and Greenland. They form through a combination of offshore winds blowing from nearby ice sheets and warm water rising from the deep ocean. In areas of extreme cold and little access to food, polynyas provide an oasis for marine mammals to survive and they are also critical for global ocean circulation.

“Polynyas in the polar regions are common nowadays, but it’s difficult to confirm their existence in the past. However, by finding chemical fossils of algae that live in the open ocean and in sea ice, we have shown that polynyas must have existed during the last Ice Age,” says co-author Simon Belt, professor of chemistry at Plymouth University. 

During a subsequent period of abrupt climate change around 17,500 years ago, cold freshwater from the melting ice caps caused entire northern oceans to be covered by thick sea ice, and the polynya disappeared. This resulted in a dramatic decline in marine life.  It took up to 2,000 years for life to recover.

The research is of international importance since it shows the vulnerability of marine ecosystems in the northern oceans to periods of rapid climate change, as well as their adaptability to various extreme climate states.

Reference 

Knies, J., Köseoğlu, D., Rise, L., Baeten, N., Bellec, V.K., Bøe, R., Klug, M., Panieri, G., Jernas, P.T., Belt, S.T. (2018). Nordic Seas polynyas and their role in preconditioning marine productivity during the Last Glacial Maximum, Nature Communications, doi: 10.1038/s41467-018-06252-8.

BBC: Vast East Antarctic iceberg from Mertz Glacier tongue 'threatens marine life'

Vast Antarctic iceberg 'threatens marine life'

BBC News, February 26, 2010

How the new iceberg was formed 7 January 2010: B9B iceberg, which is 97km long, approaches the Mertz Glacier tongue. 7 February 2010: the B9B iceberg makes contact with the tongue, which already had major rifts in it. 20 February 2010: the Mertz Glacier tongue breaks off creating another massive iceberg. A vast iceberg that broke off eastern Antarctic earlier this month could disrupt marine life in the region, scientists have warned. They say the iceberg, which is 78 km long and up to 39 km wide, could have consequences for the area's colonies of emperor penguins. The emblematic birds may be forced to travel further afield to find food. The iceberg calved from the Mertz Glacier Tongue after it was hit by another huge iceberg, called B9B. "It is a very active area for algae growth, especially in springtime," explained Dr Neal Young from the Australia-based Antarctic Climate and Ecosystems Co-operative Research Centre. Iceberg 'size of Luxembourg' threat "There are emperor penguin colonies about 200-300 km away to the west. They come to this area to feed, and seals in the area also come to get access to the open water," he told BBC News. He suggested that a change in the availability of open water could affect the rate of food production, which would have an impact on the amount of wildlife it could sustain. "If the area gets choked up (with ice), then they would have to go elsewhere and look for food." Changing landscape The calving of the iceberg, which has an estimated mass of 700-800 bn tonnes, has changed the shape of the local geography, Dr Young explained. Large icebergs always attract a lot of attention due to their scale Dr Mike Meredith, British Antarctic Survey "We have got two massive icebergs that -- end to end -- create a fence of about 180 km. "So the area's geography has changed from a situation where we effectively had a box in which two sides were open ocean," he told BBC News. "Now we have a fence across one side of the box." Before the formation of the iceberg, the Mertz Peninsula provided the right conditions for a polynya -- an expanse of open water surrounded by sea-ice -- to exist. "Winds blow off the coast and clear anything in that region, including sea ice, exposing open water," Dr Young explained. He added that as well as providing a feeding site for the region's wildlife, the polynia also was a key production site of "bottom water"; very cold, dense water that sinks to the ocean floor. "Sea ice is relatively fresh compared to sea water, so the more sea ice you have (in the surrounding area), the more salt that is left in the remaining open water." The rise in the concentration of salt increases the water's density, causing it to sink to the bottom of the ocean. "This area around the Antarctic coastline, of which the Mertz Peninsula is one part, produces about one quarter of the Antarctic's bottom water, but the Mertz polynia is a major contributor," Dr Young said. He added that the new iceberg had shortened the length of the Mertz Glacier Tongue, which could result in pack ice entering the area and disrupting the polynia. "That means that the bottom water production rate... will decrease. "The bottom water spills over the continental shelf, flows down the continental slope into the deep ocean." This process helps drive the "conveyor belt" of currents in the Southern, Pacific and Atlantic Oceans. Any disruption to the net flow of bottom water could result in a weakening in the deep ocean circulation system, which plays a key role in the global climate system. 'Natural laboratory' However, the researchers say the changes to the region triggered by the formation of the new iceberg will not shut down the circulation system or affect the world's climate. "Large icebergs always attract a lot of attention due to their scale," observed Dr Michael Meredith from the British Antarctic Survey, who was not involved in the research. "Bottom water is indeed an important part of the global ocean overturning circulation and hence climate," he told BBC News. "There are also a number of other locations of bottom water formation, however. So, it's unlikely that a large-scale sustained change of the order of magnitude required for a global climate impact will happen from this one event. "The more important thing, I think, is that this event has been closely and carefully monitored by scientists, who will now look at the processes whereby such calvings can impact on the ocean and the ecosystem -- and studying this natural laboratory will add to our knowledge of how the Antarctic system works." Link:  http://news.bbc.co.uk/2/hi/science/nature/8538060.stm

Mammoth iceberg from the Mertz Glacier Tongue, East Antarctica, could alter ocean circulation

Mammoth iceberg could alter ocean circulation: study

by Marlowe Hood, AFP, February 25, 2010

In this satellite image released by Commonwealth of Australia, a 97-kilometer (60-mile) long iceberg known as B9B, right, is about to crash into the Mertz Glacier Tongue, left, in the Australian Antarctic Territory on Jan. 7, 2010. The collision created a new 78-kilometer (48 mile) long iceberg. (AP Photo/Commonwealth of Australia)

A aerial view of the Mertz Glacier tongue breaking off from a glacier in Antarctica after being rammed by another giant iceberg, February 20, 2010. REUTERS/Neal Young/Australian Antarctic Division

PARIS (AFP) – An iceberg the size of Luxembourg knocked loose from the Antarctic continent earlier this month could disrupt the ocean currents driving weather patterns around the globe, researchers said Thursday.
While the impact would not be felt for decades or longer, a slowdown in the production of colder, dense water could result in less temperate winters in the north Atlantic, they said.

The 2550 square-kilometre (985 square-mile) block broke off on February 12 or 13, 2010, from the Mertz Glacier Tongue, a 160-kilometer spit of floating ice protruding into the Southern Ocean from East Antarctica due south of Melbourne, researchers said.

Some 400 metres (1300 feet) thick, the iceberg could fill Sydney Harbour more than 100 times over.

It could also disturb the area's exceptionally rich biodiversity, including a major colony of emperor penguins near Dumont d'Urville, site of a French scientific station, according to the scientists.

"The ice tongue was almost broken already. It was hanging like a loose tooth," said Benoit Legresy, a French glaciologist who has been monitoring the Metz Glacier via satellite images and on the ground for a decade in cooperation with Australian scientists.

The billion-tonne mass was dislodged by another, older iceberg, known as B9B, which split off in 1987.
Jammed against the Antarctic continent for more than 20 years, B9B smashed into the Metz tongue like a slow-motion battering ram after it began to drift.

Both natural cycles and manmade climate change contribute to the collapse ice shelves and glaciers.
Tide and ocean currents constantly beat against exposed areas, while longer summers and rising temperatures also take a toll.

"Obviously when there is warmer water, these ice tongues will become more fragile," said Legresy, who works at the Laboratory for Geophysics and Oceanographic Space Research in Toulouse, southern France.

The Metz Glacier Tongue, fitted with GPS beacons and other measurement instruments, could provide crucial insights into how these influences should be apportioned.

"For the first time, we will have a detailed record of the full cycle of a major calving event -- before, during and after," he said.

Since breaking off, the iceberg -- along with the newly mobile B9B, which is about the same size -- have moved into an ajoining area called a ploynya.

Distributed across the Southern Ocean, ploynyas are zones that produce dense water, super cold and rich in salt, that sinks to the bottom of the sea and drives the conveyor-belt like circulation around the globe.

If these icebergs move east and run aground, or drift north into warmer climes, they will have no impact on these currents.

"But if they stay in this area -- which is likely -- they could block the production of this dense water, essentially putting a lid on the polynya," Legresy explained.

The Metz Glacier Polynya is particularly strong, and accounts for 20% of the "bottom water" in the world, he added.

Eventually, the icebergs will die a natural death, but their lifespan depends on where they go.
Adrift, they could melt in a could of decades. If they remain lodged against the Antarctic landmass, they could persist far longer.

Link:  http://news.yahoo.com/s/afp/20100225/sc_afp/climatewarmingglacierantarcticaiceberg